5 Biggest Green Tech Companies in the World

3. NRG Energy Inc (NYSE:NRG)

Annual Revenue: $31.54B

NRG Energy, Inc is a Houston, Texas-based American energy company. Originally the wholesale arm of Northern States Power Company (NSP), it became independent in 2000 after NSP became Xcel Energy. NRG is engaged in energy generation and retail electricity and offers a diverse portfolio including natural gas, coal, oil, nuclear, wind, utility-scale, and distributed solar generation. They serve approximately 6 million retail customers across 24 US states.